Multiply triggered spark gap



Sept. 14, 1965 H. E. SPINDLE MULTIPLY TRIGGERED smnx GAP Filed Oct. 16. 1961 POWER F I SUPPLY I lg.

SOURCE WW PULSE AMPLIFIER SENSING NETWORK 36 Fig.3

III

INVENTOR Harvey E. Spindle ATTORNEY WITNESSES United States Patent 3,206,644 MULTIPLY TRIGGERED SPARK GAP Harvey E. Spindle, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 16, 1961, Ser. No. 145,403 2 Claims. (Cl. 317-46) The present invention relates to spark gap devices and more particularly to an improved trigger gap arrangement for protecting a load in electrical apparatus.

High voltage discharge gaps employing auxiliary or trigger electrodes mounted adjacent the face of one of the main electrodes of the discharge gap have been known in the art for some time. The so-called trigger electrode is provided to reduce the working voltage of the main gap. For example, if the spacing of the main gap electrodes is such as to cause the breakdown or sparkover voltage at some fixed voltage, as for example, 100 kv., it can be triggered by a small spark between the trigger electrode and one of the main gap electrodes so that it will break down at some lower voltage as for example, 80 kv. The function of the trigger gap is to ionize the main discharge gap. Increasing the current increases ionization. Therefore, if the current in the trigger gap is increased, the voltage at which the main gap will break down is lower. These discharge gaps or spark gap devices are often employed to protect either a load or a power source in case of failure such as, for example, in ternal short-circuiting in the load.

In the conventional use of this type of spark gap device for preventing or protecting against internal faults in the load, as for example short'circuited electronic tubes, the gap is connected across the load and is subjected to the full voltage applied to the load. In case of a short circuit in the load, a means is employed to fire the trigger electrode thereby lowering the sparkover voltage in the main gap structure to a value lower than the applied voltage. Sparkover of the gap shunts the load and prevents further current from flowing therethrough. As is often the case, a single power source supplies a plurality of parallel loads. In the past, a separate discharge gap was needed to protect each load. It is sought to improve the prior art of protective spark gap devices by this invention in that a single spark gap device can be employed to protect a plurality of loads supplied from a single source.

The principal object of the present invention is to provide an improved protective discharge gap for electrical equipment by which a plurality of parallel loads can be protected with a single gap device,

Another object of the present invention is to provide a circuit for triggering a protective discharge gap which can initiate sparkover of the gap and bypass a plurality of parallel loads upon occurrence of a fault in any single one of the parallel loads.

Another object of the present invention is to provide a protective discharge gap which can be triggered to fire at a voltage lower than its normal sparkover by a fault in any one or more of a plurality of loads being protected by the gap.

Other objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawings, in which:

FIGURE 1 is a circuit diagram including a diagrammatic sectional view of the discharge gap embodying the invention;

FIG. 2 is a partial front elevational view of a main electrode of a discharge gap embodying the invention; and

FIG. 3 is a partial sectional view on line III--III of FIG. 2.

.within the tickler electrode 24. A

' by an insulating member 40.

Briefly, there is herein illustrated and described a circuit including two loads, as for example, high voltage electron tubes, operating in parallel from a direct-current power source. The loads are protected from internal short circuits by having a spark gap comprising a pair of electrodes spaced apart and connected across the loads. Upon the occurrence of a short circuit or other fault in the load, the gap will sparkover and shunt the load. Two separate trigger electrodes are provided in one of the main electrodes of the protective discharge gap and are operated from the taps of two similar resistors each in series with one of the loads, so that when a fault develops in either load, the voltage across the tap of the appropriate resistor will produce the trigger spark to fire the main discharge gap.

Referring now to the drawings, there is shown a power source 10 supplying loads 12 and 14 connected in parallel. Shunted across the voltage source 10 are a pair of main discharge electrodes 16 and 18, respectively, forming a discharge gap 20. The main discharge electrodes 16 and 8 may be, preferably, of spherical configuration having smooth, polished surfaces of conducting material.

Openings 22 and 23 are provided centrally in each main discharge electrode 16 and 18, respectively. The electrode 16 may be of any suitable construction according to the broader aspects of this invention, but in its more specific aspects it may be constructed as more fully described in application Serial No. 110,699 by Harvey E. Spindle, filed May 17, 1961, now Patent No. 3,114,077, issued December 10, 1963, and assigned to the assignee of the present invention,

As described in more detail in the above-mentioned copending application, the main discharge gap 16 may include a tickler electrode 24 of cylindrical configuration which extends longitudinally through the electrode to a point adjacent the periphery of the opening 22, and a trigger electrode 26 which may be a solid rod disposed current discharge means, as for example, capacitor 29 is electrically connected between the main discharge electrode 16 and the trigger electrode 26. The tickler electrode 24 is connected to the main discharge electrode 16 through a resistor 25. The electrode assembly 21 formed by the tickler electrode 24, the trigger electrode 26 and insulation 28 therebetween is supported adjacent the end of the electrode assembly The insulating member adjacent the opening 22 may be an insulation disc having a central opening for receiving the electrode assembly 21.

A sensing network 36 of any suitable type may be provided to sense faults or other undesirable characteristics in the voltage source or the load. When sensing network 36 detects a fault, it supplies a relatively low voltage signal to a pulse amplifier 38. The pulse amplifier in turn amplifies and applies its output to the tickler electrode 24. A voltage stress between the trigger electrode 26 and the main discharge electrode 16 is maintained by power supply 44. When a low voltage pulse from the pulse amplifier is applied to the tickler electrode 24, sparkover occurs between tickler electrode 24 and the main electrode 16. This sparkover ionizes the air in the trigger gap. The ionized air in this region reduces the sparkover potential of the trigger gap causing it to sparkover at its normal bias potential. The capacitor 29 which is a low inductance capacitor, discharges at high current relative to the tickler gap current causing a high current discharge in the trigger gap. This high current discharge is sufiicient to ionize the air in the main discharge gap, thereby sufliciently reducing the sparkover potential of the main discharge gap 20 to cause it to sparkover at between and of the normal sparkover potential of the main discharge gap. The sparkover of the main discharge gap shunts the load thereby removing the source voltage. It should be noted, however, that the discharge gap 20 will continue to conduct until some external equipment is actuated to open the source voltage circuit.

As can be seen in FIG. 1, the loads 12 and 14 operate in parallel from the power source 10. A triggering device 45 is provided in electrode 18 to initiate sparkover of the main gap 26 in case of an internal short circuit or other failure in the parallel loads 12 and 14. As illustrated in FIG. 1 and hereinafter described, this circuit is unique in that a single main gap can be employed to protect two or more loads. In this circuit the two devices or loads 12 and 14 are to be protected from destruction due to internal short circuits by having the main gap 20 short circuit the source. As illustrated, a pair of trigger electrodes 46 :and 48 are provided and extend parallel to the axis of the semi-spherical electrode 18 and are received in an insulator 50 which is in turn received in the opening 23 of the electrode 18. Although only two trigger electrodes 46 and 48 are illustrated, it will of course be understood that any number of trigger electrodes may be provided and that at least one electrode for each load to be protected by the gap 20 is essential.

In series with each load 12 and 14, there is a resistor 52 and 54, respectively. The electrodes 46 and 48 are connected by leads 47 and 49 to taps on the resistors 52 and 54, respectively. Thus, the electrodes 46 and 48 are maintained at a potential different from the potential of the main electrode 18. When the increase of current to either load 12 or 14 is sufiicient to provide a voltage across the resistor 52 or 54 in series with that load which exceeds the sparkover potential between either electrode 46 or electrode 48 and the main discharge electrode 18, the trigger gap will sparkover. The sparkover between one of trigger electrodes 46 or 48 and the main discharge electrode 18 will produce ionized air in the gap space 20, thereby reducing the sparkover potential between electrodes 16 and 18 and resulting in sparkover of the main discharge gap. Sparkover of this gap will shunt the source 10 thereby protecting the load from damage due to over-current.

The construction of the insulator 50 in the trigger electrode assembly 45 is a critical factor in achieving the objectives of this device. As can be seen clearly in FIGS. 2 and 3, insulator 50 is a cylindrical tube of suitable insulating material. The tube 50 includes an electrode separator 50a which is a dividing wall extending diametrically across the tube and extending for the length of the insulating tube 50. A single electrode separator is shown in the embodiment illustrated, for illustrative purposes, and it will be understood that where more than two trigger electrodes are employed with more than two loads additional walls or electrode separators 50a will be provided. The separator 50a is of greater width than the cylinder wall. This is essential in order that the insulation level between the trigger electrodes 46 and 48 be higher than the insulation level between either electrode 46 or electrode 48 and the main discharge electrode 18. In this arrangement the trigger spark will be between the appropriate trigger electrode 46 or 48 and the main discharge electrode 18. The two trigger electrodes 46 and 48 will be isolated from each other under normal operating conditions and up to the time that the gap 28 is triggered. The insulation between the main discharge electrode 18 and the electrodes 46 and 48 should be good enough to withstand the normal voltage drop to the tap of either resistance 52 or resistance 54 and the insulation between electrodes 46 and 48 should be approximately twice this. The electrodes 46 and 48 are each received in the tubular semicylindrical openings in the insulator 50 formed by the wall 50a and the portion of the cylindrical Wall 58. Conductors 47 and 49 may be secured in the electrodes 46 and 48 in any suitable manner, as for example by a threaded connection as shown in FIG. 3 at 56 and 58, respectively. As shown 4 in the drawings, an insulating compound is molded around the leads 47 and 49 as shown at 68. The leads pass through the semispherical main discharge electrode 18 and are connected in the structure as shown.

The operation of the protective discharge gap should be apparent from the above description. The main discharge gap 20 formed by electrodes 16 and 18 is connected across the source which supplies parallel connected loads 12 and 14. Parallel connected loads 12 and 14 have in series, resistors 52 and 54, respectively. Conductors 47 and 49 are tapped into resistors 52 and 54, respectively, and are secured and electrically connected to trigger electrodes 46 and 48. When an internal short or other failure which may cause over-current in the loads occurs, the voltage across the resistors 52 and 54 increases thereby increasing the voltage drop between either electrode 46 or 48 and the main discharge electrode 18 depending upon where the fault occurs. The resistors 52 and 54 are normally of such value as to permit the trigger electrodes to withstand the normal voltage drop to the tap. When the voltage drop across either resistance 52 or resistance 54 increases due to over-current in the load, the corresponding electrode 46 or 48 sparks over to the main discharge electrode 18. This discharge ionizes the air in the gap space 20 and the main discharge electrode 16 and 18 spark over, thereby short circuiting the source and effectively removing the voltage from the load. Thus, a rapidly acting protective gap is provided which is sensitive to internal shorts and other failures resulting in over-current in either one or both of the loads connected in parallel.

It should now be apparent that a high voltage protective gap has been provided which has many advantages. The new protective gap and its associated trigger electrode arrangement is of simple and economical construction. It is so constructed that a plurality of loads supplied by a single source may be protected by a single spark gap device. While a particular embodiment of the invention has been shown and described for the purpose of illustration, it will be apparent that various other embodiments are possible within the scope of the invention. Thus, for example, more than two parallel loads supplied by a single source may be protected by a single gap which utilizes at least as many trigger electrodes as there are loads. While the resistances 52 and 54 are shown in series with the load, other impedance means may be employed. Inductive impedance may be employed in which case the trigger electrodes will respond to the rate of rise of current in the loads. Similarly, numerous other modifications and embodiments will be apparent to those skilled in the art and all such modifications and embodiments are within the scope of the invention.

I claim as my invention:

1. Electrical apparatus including a source of power, a plurality of loads supplied by said source, a pair of main discharge electrodes spaced apart to form a protective discharge gap connected in parallel with said loads, one of said main discharge electrodes having a plurality of trigger electrodes disposed adjacent the discharge path of said protective discharge gap, each of said trigger electrodes including means for connecting to a load to be protected, impedance means in series with each load intermediate said one main discharge electrode and the load, one of said trigger electrodes being connected intermediate said impedance means and the load whereby the potential dilierence between the trigger electrode and said one main discharge electrode varies directly with the current through the load.

2. A spark gap device for protecting electrical apparatus including a power source and a plurality of load devices supplied by said source, said spark gap device comprising a pair of main electrodes spaced apart to form a single protective discharge gap connected across said load devices, one of said main electrodes having a central opening therein, an insulating member received in said opening, a plurality of trigger electrodes supported in said insulating member and insulated thereby from each other and from said one main electrode, the trigger electrodes being disposed to form trigger gaps with said one main electrode and being spaced from each other a greater distance than the spacing between each trigger electrode and the main electrode, and means for connecting each trigger electrode to respond to a predetermined abnormal condition of one of said load devices to independently initiate spark-over of the protective discharge gap.

References Cited by the Examiner UNITED STATES PATENTS GEORGE N. WESTBY, Primary Examiner. ARTHUR GAUSS, Examiner. 

1. ELECTRICAL APPARATUS INCLUDING A SOURCE OF POWER, A PLURALITY OF LOADS SUPPLIED BY SAID SOURCE, A PAIR OF MAIN DISCHARGE ELECTRODES SPACED APART TO FORM A PROTECTIVE DISCHARGE GAP CONNECTED IN PARALLEL WITH SAID LOADS, ONE OF SAID MAIN DISCHARGE ELECTRODES HAVING A PLURALITY OF TRIGGER ELECTRODES DISPOSED ADJACENT THE DISCHARGE PATH OF SAID PROTECTIVE DISCHARGE GAP, EACH OF SAID TRIGGER ELECTRODES INCLUDING MEANS FOR CONNECTING TO A LOAD TO BE PROTECTED, IMPEDANCE MEANS IN SERIES WITH EACHLOAD INTERMEDIATE SAID ONE MAIN DISCHARGE ELECTRODE AND THE LOAD, ONE OF SAID TRIGGER ELECTRODES BEING CONNECTED INTERMEDIATE SAID IMPEDANCE MEANS AND THE LOAD WHEREBY THE POTENTIAL DIFFERENCE BETWEEN THE TRIGGER ELECTRODE AND SAID ONE MAIN DISCHARGE ELECTRODE VARIES DIRECTLY WITH THE CURRENT THROUGH THE LOAD. 